A Wire Bonder is a machine with which wire connections are made to semiconductor chips after they have been mounted on a substrate. The Wire Bonder has a capillary which is clamped to the tip of a horn. The capillary serves to secure the wire to a connection point on the semiconductor chip and to a connection point on the substrate as well as to guide the wire between the two connection points. On making the wire connection between the connection point on the semiconductor chip and the connection point on the substrate, the end of the wire protruding from the capillary is first melted into a ball. Afterwards, the wire ball is secured to the connection point on the semiconductor chip by means of pressure and ultrasonics. In doing so, ultrasonics are applied to the horn from an ultrasonic transducer. This process is known as ball bonding. The wire is then pulled through to the required length, formed into a wire loop and welded to the connection point on the substrate. This last process is known as wedge bonding. After securing the wire to the connection point on the substrate, the wire is torn off and the next bond cycle can begin.
The ball bonding is influenced by various factors. In order to achieve bond connections of a predetermined quality, the adequate values of several physical and/or technical parameters must be determined for a particular process. Examples of such parameters are:                the bond force, that is the normal force which the capillary exerts on the ball bond or the connection point of the semiconductor chip during the bonding process,        a parameter, designated herein as ultrasonic variable P, which controls the application of ultrasonics to the ultrasonic transducer. The ultrasonic variable is, for example, the amplitude of the alternating current which flows through the ultrasonic transducer of the horn or the amplitude of the alternating voltage which is applied to the ultrasonic transducer, or the power, or another variable,        a time duration, designated herein as ultrasonic time T, which indicates the length of time that the ultrasonic variable P is applied to the ultrasonic transducer,        the impact velocity of the capillary on the connection point,        a binary parameter that indicates whether the ultrasonic variable is already applied to the ultrasonic transducer before the capillary impacts on the connection point.        
A method for determining optimum bond parameters is known from U.S. Pat. No. 3,458,921. With this method, several bonding operations are carried out whereby the bond parameters to be optimised are each varied in a predefined range in discrete steps. Afterwards, the connections are subjected to a shear or pull test and that bonding operation is determined which gave the best test results.